Cardiac stents, which are an example of a self-expanding device, are inserted into a blood vessel to provide an open path within the blood vessel, have been widely used in intravascular angioplasty treatment of occluded cardiac arteries, and in other applications. Stents are often deployed by use of inflatable balloons, or mechanical devices which force the stent open, thereby reinforcing the artery wall and provide a clear through-path in the center of the artery after the angioplasty procedure to prevent restenosis. The use of placement techniques, such as balloons or mechanical expansions of the type often found to be useful in cardiac surgery, are relatively less useful in vasoocclusive surgery, particularly when tiny vessels, such as those found in the brain, are to be treated.
Other stents are self-expanding and are just deployed inside of the vascular. Their self-expanding nature allows them to be smaller as well as the devices to deploy them. There are different techniques to deploy the stents, and each has benefits and drawbacks. One expandable stent and delivery system is known that includes an expandable stent having proximal and distal anchor members mounted on proximal and distal legs extending proximally and distally from the stent. The proximal and distal anchor members of the expandable stent are mounted in gaps formed between proximal, intermediate and distal cylindrical members disposed on and spaced apart along an elongated core member. However, pushing the device distally in a catheter from the proximal end of the device is not optimal, because application of force in a distal direction on the proximal end of the stent can axially compress the stent, and can cause the stent to expand radially. Likewise, retracting the device proximally may not be optimal either, because application of force in a proximal direction on the distal end of the stent also can axially compress the stent, and can cause the stent to expand radially.
Some known implant deployment techniques utilize members extending from a delivery wire positioned outside the stent which push against the stent proximally or distally depending on distal or proximal placement of the members in relation to the stent. See, U.S. Pat. Nos. 6,123,723, 6,280,465, and US Publication No. 2011/0307049. Other techniques deploy the members inside of the stent. See, US Publication No. 2014/0277360, and U.S. Pat. Nos. 5,702,418, and 6,955,685, all of which are incorporated herein by reference. Such techniques may result in the members of the delivery system becoming caught on a deployed implant during extraction of the delivery wire and subsequently altering the position of the implant in the anatomy. Such techniques may also require several members which can increase the likelihood of altering the position of the implant during extraction of the delivery wire. Also, the more members on the delivery wire, the more difficult it may be to manufacture. In order to build the delivery system, a manufacturer can either secure polymer/metal sleeves onto a core wire, or grind down a core wire to create members on a wire. The more members on a delivery wire, the more material must be used to add and secure members, or, the more the grind profile has to change to accommodate all of the members.
More recently, a technique employing a dual function bump member disposed on a delivery wire and positioned within an implant, and a pusher bump member disposed on the delivery wire and positioned proximal the implant can deploy and retract the implant using only the two bump members on the delivery wire. See, US Publication No. 2018/0092766, incorporated herein by reference. While this solution can address the problems of other known techniques as discussed, the technique can require pushing or pulling the delivery wire over substantial lengths during deployment and repositioning of the implant. The dual function bump member can be positioned at the distal end of the implant during deployment and moved to the proximal end of the implant for extraction. Therefore, repositioning of the implant can involve subsequent distal and proximal movements of the delivery wire that are approximately equal to the length of the implant. Particularly for longer implants, this can increase the likelihood that deployed portions of the implant may be disturbed. Additionally, a length of delivery wire approximately equal to or longer than the stent may extend between the dual function bump and the distal coil 220 so that the distal coil 220 does not interfere with the deployed implant during retraction of the implant. In some treatments, a shorter extension of the distal coil 220 may be desired.
Thus, it would be desirable to provide a delivery system for expandable stents that offers the flexibility of deploying and retracting the stent as desired with minimal travel of the delivery wire during deployment and retraction. Also desirable is a simplified manufacturing method. The solution of this disclosure solves these and other problems of the art.